I know this sounds weird, and maybe counter productive, but I grew up listening to war stories from my grandparents and their siblings. All of my great uncles, etc. Literally I have probably 20 WW2 vets in my extended family. If you know any WW2 vets, maybe he can talk to them (or someone who lived through the holocaust, or grew up in nazi Germany). theres nothing like talking to someone who was there. Talking to my uncles about liberating the Jews and others in the concentration camps was something that I will never forget... I think that may change his perspective a little bit if he can get that opportunity. Sadly children are impressionable; this isnt his fault but you dont want him to grow up being like that.